I, too, would simply take a card with a note explaining their gift has been delayed. Particularly if they have no clue a quilt is coming, you could simply say it's been delayed in shipping. If they know a quilt is coming and you'd like to be a bit creative, you could include snippets of fabrics and batting to whet their appetite. I believe per proper ettiquete rules you actually have a year in which to deliver a wedding gift.